This invention relates in general to machines for making packages and deals more particularly with an improved sealing jaw mechanism for use in a package forming machine.
In package making machines it is common to form seals in web material by moving opposing sealing jaws toward each other from an open position to a closed or sealing position wherein the web of material is squeezed therebetween. The seal may be effected in various ways, as by applying heat to the jaws in sealing position where the web is a heat sealable thermoplastic material or by applying pressure to the material with the jaws where a pressure sensitive material is employed to effect the seal. Various modified forms of sealing jaws may also be used to apply clips, staples, bands, adhesive strip or other fasteners to packaging material. The present invention concerns primarily apparatus or mechanism for operating such sealing jaws and may be used in various different types of package making machines. The mechanism of the present invention is particularly suitable for use in a vertical form, fill and seal packaging machine for making package end seals. However, it will be understood that the invention in its broader aspects is not limited to this particular packaging machine application.
In a vertical form, fill and seal machine, an advancing web of flexible thermoplastic packaging material is formed into a depending upwardly open tubular configuration, sealed longitudinally along overlapping vertically extending marginal edge portions, sealed transversely along horizontal lines spaced vertically along the tube and filled from above with measured quantities of product between successive transverse end sealing operations. The formed tube must be halted during each end sealing operation while opposing end sealing jaws move horizontally inward toward each other to flatten a portion of the tube and heat seal to one another the two layers which comprise the flattened portion. During one closing cycle of the jaws a finished package is severed from the tube thereabove, which is being simultaneously filled. During each package forming cycle the tube must remain at rest while the end sealing jaws move from an open position wherein the jaws are spaced a sufficient horizontal distance apart to allow the tube to pass downwardly therebetween to a sealing position wherein the jaws compress and seal the package and return to open position. Consequently, the end seal forming time comprises a substantial part of the overall time interval required to produce a finished package. Actuating mechanisms heretofore available for opening and closing the end sealing jaws in a vertical form, fill and seal packaging machine generally includes a compound toggle mechanism having a large number of moving parts which impart considerable inertia to the mechanism. A typical end sealing jaw actuating mechanism for such a machine is illustrated and described in U.S. Pat. No. 4,040,237 for SEALING JAW MECHANISM FOR PACKAGE MAKING MACHINE to O'Brien, issued Aug. 9, 1977 and assigned to the assignee of the present invention. Such apparatus operates with high inertia and imposes limitations upon the speed at which a package can be formed.
Accordingly, it is the general aim of the present invention to provide an improved actuating mechanism for operating sealing jaws in a packaging machine and which is dependable, durable and employs relatively few moving parts to enable increased packaging machine operational speed.